Four-port junction circulator having larger diameter conductive post contacting gyromagnetic post

ABSTRACT

A four-port waveguide circulator includes a pair of rectangular waveguides which extend perpendicular to each other to form a junction having a pair of parallel boundary walls. A post of gyromagnetic material of a first diameter extends from one wall and a post of conductive material of a diameter greater than the first diameter extends from the other wall so as to contact the post of gyromagnetic material. The dimensions of the post of gyromagnetic material and of the post of conductive material are determined, with the strength of a magnetic field directed axially of the gyromagnetic post being selected, to produce a circulator action.

United States Patent [1 1 Jung FOUR-PORT JUNCTION CIRCULATOR HAVING LARGER DIAMETER CONDUCTIVE POST CONTACTING GYROMAGNETIC POST GYROMAGNETIC MATERIAL [451 Feb. 11, 1975 Primary Examiner-Paul L. Gensler Attorney, Agent, or Firm-Edward J. Norton; Robert L. Troike [57] ABSTRACT A four-port waveguide circulator includes a pair of rectangular waveguides which extend perpendicular to each other to form a junction having a pair of parallel boundary walls. A post of gyromagnetic material of a first diameter extends from one wall and a post of conductive material of a diameter greater than the first diameter extends from the other wall so as to contact the post of gyromagnetic material. The dimensions of the post of gyromagnetic material and of the post of conductive material are determined, with the strength of a magnetic field directed axially of the gyromagnetic post being selected, to produce a circulator action.

3 Claims, 3 Drawing Figures CONDUCTIVE POST PfxTEN'I'EU I [975 3.866.149

GYROMAG MATER BACKGROUND OF THE INVENTION This invention relates to circulators and more partic-' ularly to a four-port waveguide junction circulator.

Waveguide junction circulators find wide use in the front end of airborne avionic equipment such as weather radar. Thesecirculators function to couple energy between a common antenna and transmitter or a receiver. Although a three-port circulator can be used to perform the coupling, additional isolation of the transmitter from reflected signals is required. For example, if in a three-port junction circulator biased to couple signals in a clockwise direction the first port is coupled to a transmitter, the second port in a clockwise direction is coupled to an antenna, and the third port in a clockwise direction is coupled to a receiver, high level energy reflected at the third port will reach the transmitter and change its frequency. One way of achieving the extra isolation is by the addition of a second three-port circulator located between the third port of the first circulator and the receiver. In this case the second port of the second circulator is coupled to the receiver and the remaining third port is coupled to a load. Although this arrangement can perform satisfactorily, the additional circulator takes up space in the avionics equipment where space is at a premium. Further, the. additional circulator adds weight and adds cost. Four-port circulators take essentially no more room than three-port circulators and, if arranged properly, can provide the additional isolation between the transmitter and receiver ports by a fourth port terminated in a load located therebetween.

Four-port circulators are known. In Allin et al. U.S. Pat. No. 3,01 5,787, four-port circulation is achieved by a tuning screw extending toward and along the axis of a ferrite body or prism at the junction of four waveguides. Another way of tuning in the prior art to achieve circulation is by the placement of a conductive pin extending through the center of the ferrite body lo cated between the waveguide walls at the junction. The electric field in these structures is peaked near the center of the ferrite, whereby these structures tend to break down under relatively high powers such as that provided by the transmitter for a weather radar, for example. A high power, four-port circulator operable at the 9.305 to 9.415 GHz frequency band, for example, with powers on the order of 60 KW at the transmitter has not been achievable using prior art techniques. Although three-port circulators with this capability are known, there exists no simple theorem for junctions having more than three ports.

BRIEF DESCRIPTION OF THE INVENTION A four terminal waveguide circulator comprises a pair of rectangular waveguides extending in perpendicular relationship in a common plane to form a junction having a pair of parallel boundary walls. A cylindrical post of gyromagnetic material of a first diameter is disposed within the junction of the waveguides on one of the boundary walls at the center of the junction. The axis of cylindrical post of gyromagnetic material is arranged normal to the common plane with the axial length of the post of gyromagnetic material being less than the distance between the boundary walls. A cylindrical conductive post of a diameter greater than the diameter of the gyromagnetic postis disposed within the waveguide junction on the other of the boundary walls, with the axis of the conductive post being normal to the common plane and extending to the gyromagnetic post. The diameter and height of the cylindrical conductive post and of the gyromagnetic post, together with the strength of a magnetic field applied axially of the gyromagnetic post, are determined to produce a desired circulator action.

DETAILED DESCRIPTION A detailed description follows in conjunction with the following drawing:

FIG. 1 is a simplified drawing of a four-port rectangular waveguide circulator according to the present invention.

FIG. 2 is a top plan view of a four-port rectangular waveguide circulator according to one preferred embodiment of the present invention.

FIG. 3 is a cross-sectional view of the circulator of FIG. 2 taken along the 3-3 axis.

Referring to FIG. 1, a simplified view of applicants four-port circulator is described. The circulator 10 comprises two rectangular waveguides 11 and 12 designed to operate in the TE mode. These rectangular waveguides l1 and 12 intersect each other intermediate their ends in perpendicular relationship in a common plane. The circulator 10 includes two waveguide arms 14 and 15 at opposite ends of waveguide 11, two waveguide arms 16 and 17 at opposite ends of waveguide 12, and a common junction region 13 with parallel boundary walls 25 and 27. The waveguide arms are arranged in a common H or magnetic field plane. The angle between each of the arms is a right angle.'Within the center of the junction 13 of the circulator is placed a cylindrical body or post 18 of gyromagnetic material. The post 18 extends from the bottom boundary wall 27 of the junction 13 as shown by dashed lines in FIG. 1 toward the center of the junction 13. Directly above and connected to the top boundary wall 25 is located a larger diameter post 20 of conductive material.

The term gyromagnetic" material as used herein refers to ferrimagnetic, ferromagnetic and antiferromagnetic material, which materials exhibit a phenomenon associated with the motion of dipoles in these materials, which in the presence of a DC magnetic field is similar in many respects to the classical gyroscope. These materials and their properties are discussed by Lax and Button in Chapters 1 thru 6 of their book entitled Microwave Ferrites and Ferrimagnetics, published in 1962 by McGraw Hill, New York, USA. The most commonly used gyromagnetic materials are ferrites and garnets.

In order for the device 10 to act as a circulator so that electromagnetic energy entering from a transmitter, for example, at arm 14 will be coupled to an antenna coupled at port 16, for example, and not to a receiver coupled to port 15 or to a load at port 17, proper magnetic d.c. (direct current) bias is provided in the direction of arrow 21. This may be provided by permanent magnets located on opposite sides of the junction 13.

Referring to FIGS. 2 and 3, a preferred form of the waveguide circulator is shown. A conductive body 10a has channels 14a, 15a, 16a and 17a formed therein. These channels are of appropriate size to form the rect- 3 angular waveguide arms operable in the TE mode and the channeled void at the junction 13a of these arms 14a, 15a, and 17a. The junction 13a is bounded by a top wall 25a and bottom wall 27a.

A cylindrically shaped body or post 180 of gyromagnetic material extends in a perpendicular manner from the bottom wall 27a of the circulator a. See FIG. 3. The lengthwise axis of the post 18a extends through the center of the junction 13a which center is the intersection of the center lines of the channels 14a, 15a, 16a and 17a. The diameter d of the post 18a is approximately equal to one-third the width of the waveguide channels and has a length I along the axis perpendicular to bottom wall 270 equal to about one-fourth to threefourths the narrow dimension of the waveguides formed by the channels.

A second larger diameter conductive post 200 extends from the opposite top broad wall 25a of the waveguide at the junction region 13a. This post 20a as shown in FIG. 3 can be a cylindrically shaped raised step formed by extending the top wall a about the region of the junction 13a. This cylindrical conductive post may be provided by channeling the junction at less than the full waveguide height. The cylindrical post 20a presents a totally conductive surface and is of a diameter D in FIG. 3 equal to about the entire wide dimension of the waveguide channels. The conductive post 20a is centered in the junction 13a and extends a distance h to the body or post 18a of gyromagnetic material also centered in the junction 13a. The gyromagnetic post 18a and the conductive post 20a are centered on an axis which intersects the center lines of the waveguides formed between channels.

An external magnetic field is applied along and parallel to the cylindrical axis of the ferrite post 18a. This magnetic field is provided in the preferred embodiment shown in FIGS. 2 and 3 by a pair of magnets 31 and 32 located at opposite ends of the gyromagnetic post 18a. The body 10a has a channel 35 that extends through the top wall 25a including a portion of the conductive post 20a. A similar channel 37 is located in the bottom wall 27a of body 10a. In each case the channels 35 and 37 do not extend to the gyromagnetic post 18a. The magnets 31 and 32 are secured in these channels 35 and 37 by suitable bonding material.

The values for the dimensions of the gyromagnetic post and of the conductive post are determined as follows:

1. Select an initial value for the diameter d of the gyromagnetic post 18a. This value can be found from 2.65 equals K R where K is the wave number of the electromagnetic field in the post and R equals half the diameter of the gyromagnetic post 18. The length I is made on half the height of the waveguide arms.

2. Select an initial value for the diameter D of the conductive post 20a by assuming the circulator structure to form a radial transmission line, the length of which is to be adjusted for resonance. Make the height h equal to one half the height of the waveguide arms.

3. Adjust the diameter D of the post 20a and the magnetic field to minimize the reflection at the circulator of applied energy incident at each waveguide arm out of that same waveguide arm.

4. If the insertion loss between ports is high, change the diameter d of the gyromagnetic post 18a until insertion loss is minimized between these ports. Repeat steps 1 thru 3 until all ports are matched.

A four-port circulator like that described above in FIGS. 2 and 3 was operatedover a frequency range of 9.305 to 9.415 GHz. The insertion loss was less than 0.3 db and the isolation was greater than 21 db between ports. It was operated at greater than 60 kilowatts at sea level and at greater than 8 KW at 60,000 feet attitude over a temperature range of -55C to C.

The circulator has the following dimensions: the waveguide arms 14a, 15a, 16a and 17a are conventional WR- rectangular waveguides with the narrow wall height being about 0.400 inch and the broad wall width 0.900 inch. The body material was an aluminum alloy.

The diameter d of the gyromagnetic body 18a is 0.290 inch and the length I along the perpendicular axis to wall 27a is 0.200 inch. The material of body 18a is Trans-Tech G4257 garnet with a dielectric constant of about 15.2. Trans-Techs address is 12 Meem Ave., Gaithersburg, Maryland 20760.

The diameter D of the conductive post is 1.15 inch and the height h is 0.200 inch. the diameter D is over a half wavelength greater than diameter d. The magnets 31 and 32 are spaced about 0.020 inch from the garnet post 18a. The magnets 31 and 32 are each about 0.5 l 6 inch in diameter and 0.400 inch thick, are alnico 8 material, and may be obtained from Arnold Engineering, Marengo, Ill. 60152.

What is claimed is:

1. In a four terminal waveguide circulator operable over a given frequency range comprising a pair of rectangular waveguides extending in perpendicular relationship in a common plane to form a junction having a pair of parallel boundary walls, separated from each other by a height equal to the height of each of said waveguides, and a cylindrical post of gyromagnetic material of a first diameter disposed within said junction of said waveguides between said boundary walls and on one of said boundary walls at the center of said junction, the axis of said post of gyromagnetic material being normal to said plane and the axial length of said post of gyromagnetic material being less than the distance between said boundary walls, and means for providing a magnetic field directed axially of said post of gyromagnetic material, the improvement therewith comprising:

a cylindrical conductive post of a diameter greater than said first diameter by an amount at least approximately a half wavelength at a frequency within said give frequency range disposed between said boundary walls at said junction and on the other of said boundary walls, the axis of said conductive post being normal to said plane with said conductive post extending to contact said post of gyromagnetic material, the gyromagnetic post and the conductive post being centered on an axis which intersects the center lines of said waveguides, the relative heights and the diameters of said posts being dimensioned with a given strength of said magnetic field to provide circulator action.

2. The combination claimed in claim 1 wherein the diameter of said conductive post exceeds the diameter of said gyromagnetic post by a length equal to a half wavelength at a frequency within said given frequency range.

3. The combination claimed in claim 2 wherein the diameter of said conductive post is approximately equal to the width of said rectangular waveguides. 

1. In a four terminal waveguide circulator operable over a given frequency range comprising a pair of rectangular waveguides extending in perpendicular relationship in a common plane to form a junction having a pair of parallel boundary walls, separated from each other by a height equal to the height of each of said waveguides, and a cylindrical post of gyromagnetic material of a first diameter disposed within said junction of said waveguides between said boundary walls and on one of said boundary walls at the center of said junction, the axis of said post of gyromagnetic material being normal to said plane and the axial length of said post of gyromagnetic material being less than the distance between said boundary walls, and means for providing a magnetic field directed axially of said post of gyromagnetic material, the improvement therewith comprising: a cylindrical conductive post of a diameter greater than said first diameter by an amount at least approximately a half wavelength at a frequency within said give frequency range disposed between said boundary walls at said junction and on the other of said boundary walls, the axis of said conductive post being normal to said plane with said conductive post extending to contact said post of gyromagnetic material, the gyromagnetic post and the conductive post being centered on an axis which intersects the center lines of said waveguides, the relative heights and the diameters of said posts being dimensioned with a given strength of said magnetic field to provide circulator action.
 2. The combination claimed in claim 1 wherein the diameter of said conductive post exceeds the diameter of said gyromagnetic post by a length equal to a half wavelength at a frequency within said given frequency range.
 3. The combination claimed in claim 2 wherein the diameter of said conductive post is approximately equal to the width of said rectangular waveguides. 